Motor OCPD

Magnettica

Just getting ready here to take the exam some time next year. I'm doing some prep using Tom Henry's Calculations 2005 book and I had a question. One of the study question's is this:

What size dual-element fuse does the code require for a 2 horsepower, 208 volt, single phase motor?

A) 20 AMP
B) 30 AMP
C) 35 AMP
D) 40 AMP

So... a 2hp motor rated at 208 volts is 13.7 amps (table 430.247)

13.7 amps x 175% (table 430.52 for dual element fuse) = 23.1 amps

I know the correct fuse size would be 25 amps, however, that answer isn't given!!

Will there be ridiculous multiple choice answers like this when I take the exam?

JamesNLA

In my experience, test taking is a skill all in itself. There are guys that say the XYZ trade test was a joke...so simple and a waste of time. While there can be a large groupe that will fail everytime. Knowing ur stuff AND good test taking skills are key. Simplest one is what is NOT the answer given to you. Kinda like troubleshooting...just a process of elimination. With the example you have, it's obviously a formula question, you know the formula, therefore you know the answer. So of those answers given to you, and the rules that apply to over current protection, the answer it there. Might not agree with it, but it is there.

__________________
"....And then we all switch places when I ring the bell"
-Adrock

Celtic

Yup....and my suggestion is to avoid them.

All questions bear the same weight, so why waste your time w/all those numbers vs. a "How many inches between supports" type of question?

Bone up all you want on the calc. type questions, but when the sheet hits the fan....take the easy grounders.

__________________

nap

well, the correct answer is: the code does not require any fuse of any size. It ALLOWS a fuse of a determined size. All of those listed would not be allowed (accepting your calcs, didn;t bother to look) except the 20 amp fuse so a 20 amp fuse would be the only one that can be used of those listed.

whoops. have to make a correction. 430.52 exc.2 allow up to a 225% fuse (time delay) to be used if needed so the 30 amp fuse is allowed as well, if needed.

InPhase277

It's actually table 430.248. But I think the answer is dependent on 430.52(C)(1) Exception 2(b). This allows a dual-element fuse to be at most 225% over the table current. 13.2 A x 225% = 29.7 A. A 30 A fuse would be right.

EDIT: Dammit! I was beaten to it.

Magnettica

I would argue that Exception No. 2 is only for when the motor has some sort nuisance tripping happening or won't start due to a large load.

InPhase277

And I would argue that that is the meaning of the question. What is the maximum dual-element fuse allowed? 30 A.

nap

but that is not the question magneticca posted.

that is why my first post said, basically, none of the above, because the code does not require any fuse of any size. It allows a fuse of a calculated size.

if you want to go with "allow" then it would have to be 30 amp becuase you can legally install up to a 30 amp fuse in that situation.

Magnettica

Hopefully, 4 years of night school will pay off when I sit in for the exam.

JamesNLA

I'm glad he got to see this. This is a prime example of Government testing. In a multiple choice setting, there is always a correct answer - wheather or not you agree with it or not doesn't matter. This is where good test taking skills come into play. I would also agree with another poster in saying don't spend too much time on any one problem. There is nothing worse than running out of time b4 you have completed everything. Good Luck Mags

__________________
"....And then we all switch places when I ring the bell"
-Adrock

Magnettica

Here's another one just for kicks...

A 5 HP, single-phase 230 volt wound rotor motor would have non-time delay fuses sized at _____ percent.

A) 300
B) 175
C) 150
D) 250

JamesNLA

A)


.

__________________
"....And then we all switch places when I ring the bell"
-Adrock

Magnettica

Tom Henry has C) 150% 430.52

InPhase277

I will say C as well, and not just 'cause Tom wrote the book

Remember that alot of questions contain "fluff". For example, "5 HP, 230 V single phase". That had absolutely nothing to do with what percentage you can oversize the fuse. They put that stuff in to throw you off.

hpp2

Save all your calculation questions till the end, then start with easy ones.
It took me 3hrs. 55 min for the 4 hr test. Know how to look things up in the code book. I took the code couse at Middlesex Collage. The instructor was pretty good.

Magnettica

I'm pretty good with the NEC and knowing where to look for answers (at least I think so). This code course you took at Middlesex, is it a class specifically for the examination or is it 1 night a week for 12 weeks like it is at Union County Vo Tech?

Btw, welcome to the forum.

SonoranShocker

Hey Mag, try this website:

www(dot)codebookcity(dot)com(slash)codearticles(sl ash)nec


It really helped me study for the exam, which is good because I am a lousy test taker...

(man how many more times do I have to post before it lets me post a friggin link?!) oh wait, I see...

__________________
Friendship is like peeing on yourself: everyone can see it, but only you get the warm feeling that it brings

mickeyco

Easier to follow link from above.



Here are some important questions from the Chicago exam.


What is the maximum fine for a commercial bakery in which an electrical inspector found a motor without a name plate, a capacitor exposed to magnesium dust, and an unlocked transformer vault after these violations have continued for two days?

A. $500
B. $1000
C. $1500
D. $3000




What is the inspection fee for 201-400 amp electrical service?

A. $75
B. $70
C. $65
D. $60



What is the price of tea in China?*








*I added that one.


.

__________________
Some people climb mountains. I take out the trash. But we both do it for the same reason.

nap

I think that is only part A of the question. Part B is

How much do you have to pay the inspector outside of legal requirements to have your service pass inspection?

pudge565

HMM I never knew you could get 208 single phase boy you learn something new everyday.